1. Field of the Invention
The present invention relates to an ink jet printing apparatus, and more particularly to a tube pump for use in an ejection recovery operation to maintain and recover the ejection performance of a printing head for ejecting ink.
2. Description of the Related Art
As printing apparatuses used on printers, copiers, facsimile machines, etc. or used as output devices for computers, ink jet printing apparatuses, which performs printing by ejecting ink onto a printing medium such as a paper, are in widespread use. On the other hand, there are various demands for the material of a printing medium for use on the apparatuses. In order to meet the demands, it is a recent practice to supply a printing apparatus on which cloth, leather, non-woven fabric metal or the like is to be used as a printing medium besides the usual printing medium of a paper, an OHP sheet or the like.
The ink jet printing apparatuses are advantageous because of low noise and running cost and easiness to reduce the size and use with colors, and hence broadly applied on printers, copiers, facsimile machines, etc. The ink jet printing apparatus is provided with a printing head having ejection openings through which ink is to be ejected. The ejection opening has a diameter of approximately several tens micrometers, and it is a recent tendency to reduce ejection opening size as print image quality is improved. The ink jet printing apparatus is to eject ink through fine ejection openings during printing, and thus clogging possibly occurs in the ejection opening thus resulting in defective ejection, e.g. failure to eject ink. When the defective ejection occurs, the resulting image is possibly lower in quality.
As a countermeasure against the defective ejection, it is a usual practice to carry out a recovery operation in order to maintain and recover the ink ejection performance of the printing head. As such recover operations, suction recovery is known in which ink is drawn out of the printing head by suction. The suction recovery includes operations to cap the ejection opening of the printing head with a cap and to cause negative pressure at the inside of the cap through the action of pumping in the capping state. This causes foreign matters such as viscous ink, bubbles to be drawn through the ejection openings of the printing head, to refresh the ink inside the ejection openings. Incidentally, as another type of recovery operation, wiping is also known to wipe and clean away foreign matters such as ink put on the ejection opening face of the printing head, subsequently to the suction recovery.
Those pumps for the suction recovery include a tube pump that generates negative pressure by utilization of the volume change at the inside of its elastic tube. More specifically, a volume change within the tube caused by pressing the tube in one direction by use of a roller or roller moving along the tube, causes negative pressure to be produced at the rear of the tube being pressed. Then, by the connection of the tube with the cap covering the ejection opening face of the printing head, ink is drawn out of the printing head through utilization of the negative pressure caused in the tube.
As a prior art of the tube pump, Japanese Patent Laid-Open No. 2001-063093 describes a structure that a tube is sandwiched between rollers in the number of n (N≦3) arranged in a peripheral edge of a rotary member and squeeze surfaces in the number of (n−1) or less, which are located opposite to the rollers and at the outside of the periphery of the rotary member, and the rotary member is rotated. In this structure, by rotating the rotary member, the rollers continuously press the tube against the squeeze surfaces to generate negative pressure.
Furthermore, Japanese Patent Laid-Open No. 6-198902 (1994) and Japanese Patent Laid-Open No. 2001-355580 describe similar structures using a plurality (N) of tubes arranged in a manner dividing, into equal parts, the inner peripheral surface of the pump case. By moving pressurizing rollers in the number of (N+1) arranged in a manner dividing into equal parts the circumference about a pump drive shaft, the tubes are deformed under pressure thereby causing pumping.
In the tube pump described in the above two prior arts, there exists portions where the two tubes are introduced on a path along which the rollers rotatively move. More specifically, there exists two introduction portions where tubes are introduced into the pump case and where the pressing by the roller is terminated. FIG. 18 is a view showing typical one form of the same. The pump shown in FIG. 18 has an inner peripheral surface of pump case 80 that is divided into two equal parts wherein elastic tubes 81, 82 are arranged along the respective ones of the inner peripheral surface. The roller holder 84, guiding the rotation shafts of three pressurizing rollers 83a, 83b, 83c, is to rotate in the arrow direction in the figure thereby causing a pumping operation. In the FIG. 18 example, two introduction portions 80a, 80b exist based on the two tubes.
The tube pump having such a plurality of tubes is for use in a suction structure that a plurality of tubes are respectively connected to a plurality of separate caps. This eliminates the necessity of providing tube pumps correspondingly to the number of caps, thus contributing to apparatus size reduction, etc.
However, the tube pump, having tube introduction portions, involves the following problems.
Firstly, in the example of FIG. 18, as the pressurizing roller 83a moves toward the introduction portion 80b, the roller 83a may drag the tube 81 in a direction of the movement while pressing the tube. As a result, the motor rotating the pressurizing rollers problematically has an increased load thereon. The problem of such a load increase becomes noticeable in the case where the motor used is small in size and output as used on the small-sized printer.
Secondly, there is a possibility to raise the following problem even where a certain countermeasure is taken against the first problem in a manner not to drag the tube. Likewise, in the example shown in FIG. 18 example, when the pressurizing roller 83a moves to the introduction portion 80b and begins reducing the pressing force on the tube, the pressurizing roller 83a, in turn, may be rebounded by the restoration force of the tube 81. In this case, the rebounded pressurizing roller 83a hits against a part of the groove on the roller holder 84 that holds the shaft of that roller. As a result, the pressurizing roller 83a temporarily takes a position unstable relative to the roller holder 84. Then the unstable pressurizing roller constitutes a cause of poor suction. In addition, the hitting sound caused by the above hitting raises noise upon driving the pump. It may be considered to use a buffer member in order to decrease such noise. This however results in a problem of cost increase because of the difficulty in the manufacture in addition to the increasing number of components.
Incidentally, the above problem is not limitedly encountered in the pump using such a plurality of tubes as disclosed in Japanese Patent Laid-Open No. 2001-063093, Japanese Patent Laid-Open No. 6-198902 (1994) or Japanese Patent Laid-Open No. 2001-355580. It is apparent from the above that the problem of dragging at the tube introduction portion or rebounding by the tube is to occur even on such a pump using one tube as described in Japanese Patent Laid-Open No. 2002-036601.